Pneumatic and liquid-containing footwear and soles have been provided in prior art that pertain to the absorption or transfer of pressure from various surfaces of the sole.
The encapsulation of air in a chamber allows the sole to provide a cushioning effect to the foot. The encapsulation of liquid in a chamber similarly provides a cushioning effect to the foot with generally less of a reactive springing quality than air due to the slower movement of liquid and their relative resistance to compression at pressures typically exerted by a human foot on the sole. Soles containing air and/or liquid (including gels and similar materials) are provided by U.S. Pat. Nos. 4,008,530, 4,219,945, 4,223,457, 4,227,320, 4,458,430, 4,670,995, 4,676,009, and 4,799,319. None of these employ the compressive qualities of encapsulated air in conjunction with the pressure-distributive qualities of encapsulated liquid.
U.S. Pat. No. 4,768,295 discloses a sole comprised of a sole member which surrounds and contains a cushioning plate having an internal pair of sheets adhered together at spacings to form a plurality of gel-filled chambers. Air chambers are formed between the filled chambers and surrounding sole plate. The sole plate, comprised of solid material, does not allow pressures on the cushioning member to be redistributed evenly over the plantar surface of the foot in conjunction with the cushioning member.
U.S. Pat. No. 4,008,530 teaches a sole having a shaped inflatable upper section mounted on a shaped lower inflatable section. Each section is fitted with valves and may be filled with air or liquid or a mixture of both. While capable of exploiting the respective benefits of liquid and air, the structure of the sole is susceptible to torsional instability and canting. There is the potential for collapse between portions of the ceilings and floors of the sections, especially when the heel or ball area of the feet strike the ground with abnormal force.
U.S. Pat. No. 4,864,737 discloses a sole having a sheet formed to provide a grid of spaced peaks connected to the roof and floor within a compartment. The sheet forms two chambers of interconnected pockets: the upper ones containing liquid, the lower ones containing air. The sheet, however, does not provide independent structural support under pressure and renders the sole vulnerable to torsional instability, canting, and internal tearing and rupture. Nor does the construction of the sole provide for control over the extent to which the properties of air and liquid are exploited; presumably, the air and liquid must be used in equal volumes.
In view of the foregoing difficulties and limitations, a sole is needed for transferring pressure from the weight-bearing portions of the foot and redistributing it over the plantar surface without introducing torsional instability, and for providing a structure wherein the respective properties of encapsulated air and encapsulated liquid are cooperatively joined in a reactive manner.